trailing comma at last element of multi-line declarations like enums or arrays

It would be nice to have a code formatter option to add a [trailing comma](https://dev.to/pfilaretov42/tiny-trailing-commas-in-java-251h) to the last element of multi-line declarations like enums or arrays.

The PDT already have such an option: [521884](https://bugs.eclipse.org/bugs/show_bug.cgi?id=521884). Unfortunately, the git links in Bugzilla does not work anymore.

Start in the Java code formatter area and trace how formatting options are defined and applied to multi-line declarations such as enums and arrays. Compare the requested behavior with PDT option 521884, then verify that the formatter can add a trailing comma only where the new option is enabled.

Written by the indexing model from the issue text.